Lighting devices, in particular when said lighting devices use light-emitting diodes (LEDs) for generating light, frequently require a cooling device by which the light sources are able to be cooled during operation, so that said light sources have a long service life and the desired lighting quality is achieved. To this end, the cooling devices generally have a preferably flat base, the LEDs being directly attached to said base or to a suitable support.
With higher outputs, passive heat sinks are no longer sufficient to ensure the desired cooling action and generally devices are used for generating a cooling media flow, which improve the dissipation of the heat output by convection. In the simplest and most common form, electrical fans which are mounted on the side of the heat sink remote from the base are used for this purpose and blow ambient air as cooling fluid approximately perpendicular to the heat sink. The cooling air flow is thus guided perpendicular to the plane of the base onto the heat sink and deflected to the side when it comes into contact with said heat sink.
Due to the deflection of the cooling air flow, greater pressures and lower flow rates result, whereby poor cooling action is achieved. If additionally the air flow is not accurately guided perpendicular to the heat sink, for example due to a slightly oblique position of the fan in relation to the heat sink, the uneven discharge of air may lead to an uneven cooling of the heat sink and thus to an undesirably uneven temperature distribution.
An optimal cooling action is particularly important in so-called retrofit lamps, which have light-emitting diodes as light sources and a conventional lamp base in order to be able to use light-emitting diodes instead of conventional incandescent lamps. Said retrofit lamps are intended to correspond in their external dimensions as closely as possible to conventional incandescent lamps and, therefore, have to have a particularly compact design and operate as far as possible in all installation positions. This promotes the occurrence of a thermal short circuit, i.e. the heated-up cooling air which has just been blown out is immediately drawn back in, particularly when the lamps are operated in spatially restricted conditions, for example due to a lamp shade.